The type-E coupler is the standard coupler for railway freight cars. As the standard coupler, all producers of such couplers in the United States are required to produce the couplers to a standard specification. Standard railway car couplers should be completely interchangeable regardless of the manufacturer. Also, couplers from any manufacturer should be able to be readily joined to couplers from any other domestic manufacturer.
The Association of American Railroads (“AAR”) has adopted standards for railway couplers. The coupler must include specific geometry and dimensions that allow it to receive a knuckle, and the geometry must be such that the knuckle is allowed to freely operate when coupling and uncoupling railway cars. These dimensions and features of the coupler may be checked for compliance with AAR standards by using gauges. When gauges are applied to a coupler in a prescribed manner, it may be verified that certain dimensions of the coupler fall within an allowable variation or tolerance range.
For example, a pulling lug gauge can be pivotably attached to a coupler similar to the attachment of a knuckle. When the pulling lug gauge is rotated into a gauging position, the pulling lugs of a coupler should be positioned in certain lug receiving portions of the gauge. This ensures that the pulling lugs are located in a position that will allow the knuckle to properly operate and interface with the pulling lugs to support the draft forces of a railroad car. Current gauges may not be suitable to test all critical dimensions of a railway car coupler.